Indeed Bugnini was involved in the reform of Holy Week. However he was not by that time President of the Liturgical Commission. The President, Mgr D'Amato, was very traditionalist, later ousted by the Modernists. He prevented the reformers of Holy Week from introducing dangers to the Faith.
Just some points of fact since your timeline seems to be quite confused. "By that time" Mgr d'Amato was not even on the very commission you claim he was president of!
Mgr d'Amato was never president of the liturgical commission involved in the Holy Week reforms, of which commission he became a member only in 1960, long after the reforms had taken place and were mandated, and even for the conciliar liturgical commission, he was only ever a member. D'Amato had absolutely nothing to do with the Holy Week reforms, and at Vatican II was more involved in the area of sacred music for the preparation of Sacrosanctum Concilium, according to the relationes.
Whether and to what extent he was involved in John XXIII's liturgical reforms leading to what we know as the 1960 breviary and 1962 missal, I do not know, but I would like to see more proof on this other than Mgr Lefebvre's personal testimony in a passing conference. It seems unlikely given that D'Amato didn't begin to become involved in the commission until 1960 itself, and then only as a member. Bugnini relates that the later members were only involved in a couple meetings.
Second point of fact, what is in our circles called "Bugnini's schema" in the preparatory stages of Vatican II's liturgical reform was not shot down by the then-president of the conciliar liturgical commission, Gaetano Cicognani, but in fact signed without changes. It was only after this episode that John XXIII removed Bugnini from his positions. But to stay to the point, Bugnini's principal work in the Pian commission had already been finished long before Vatican II.
While some traditionalists wish to downplay the role Bugnini had in these commissions, it should be remembered there were plenty of other aggressive and powerful members pushing for liturgical modernism: Augustin Bea, Carlo Braga, Ferdinando Antonelli, etc. All of these were quite open about their intentions.
The liturgical commission's work on the Holy Week, as reported by Bugnini himself as well as others, was done in complete secrecy and when published came as a surprise to the Sacred Congregation of Rites. The commission had direct access to Pius XII during his final illness because Bea, a member of the commission, was also Pius's confessor. There was absolutely no one to "prevent the reformers".
Was the new Holy Week a major conquest that Bugnini later boasted? No.
You are allowed to your opinions, but not to your facts. Bugnini boasted indeed of the Holy Week reforms and this entire period of liturgical reform multiple times in several places. He speaks of this period of the liturgical reforms as a nearly complete success and in the most effusive language, of "pearls and crowns" and "an explosion of joy". Please simply open his memoirs and read.
Braga, Bugnini's close collaborator and of the same mind, also boasted of the Holy Week reforms as "the head of the battering-ram which pierced the fortress of our hitherto static liturgy." Cardinal Antonelli, mentioned above, described it as "the most important act in the history of the liturgy from St. Pius V until today."
+Lefebvre initially complied with the '65 from his default of obedience. He noticed from certain changes (less genuflections, Signs of the Cross) that his own faith was being chipped away at. Upon noticing, he applied the principle of St. Thomas. Therefore his brief compliance with the '65 was objectively not justified, and subjectively completely justified.
Surely Bugnini and others introduced certain things with their goals in mind. However whatever things they managed to introduce in the reformed Holy Week clearly do not in themselves endanger the Faith. By '65 they had indeed inserted the first real dangers.
Again, these are strange remarks. Lefebvre was not a liturgist, as he himself would have admitted. Econe used the '65-'67 changes well into the 1970s, and the decision to stop these were prompted by the seminarians who wanted to return to a purer form of the Roman rite. Even Fr Josef Bisig of the FSSP recounts some of the stories during this period when he was a seminarian.
But the remarks are further strange because there are many Society priests even today who regularly incorporate these rubrics into their "1962" ceremonial. As I said, even senior priests of multiple districts will use rubrics from '65 and '67 without any problem, priests who were ordained in the 1990s. The Society has never been focused on the question of liturgy per se, but rather the formation of priests. Even when deciding upon 1962, it was as a matter of danger to the faith.
Lastly, it is Bugnini himself who links directly the principles that went behind the reform of Holy Week and the changes John XXIII would introduce more widely in 1960-62, changes that were the fruit of the liturgical commission.
While it is not my goal to draw a direct line of causality between these changes and a "danger to the faith," again as I said above, the line of argumentation is clearly insufficient. Liturgical scholars who have studied this time period and who try to remain impartial when discussing the history have called out how plainly the break is from tradition and the integrity of the work between 1948-1975. These are from figures as varied as Mgr Gamber, Don Alcuin Reid, Laszlo Dobszay, and more recently, the excellent work of Matthew Hazell. And again, these are not SSPX enthusiasts. If even these can see the break, why can't the Society? Well, that gets to the "baggage" I was referring to.